Air conditioning systems for motor vehicles, which have long been part of the prior art, comprise a number of individual components, such as the condenser, which is typically located at the front of the vehicle, the compressor, which is connected to and powered by the vehicle engine, the evaporator, which is located in the passenger compartment, and connecting lines. The air conditioning system conditions the air, which is then introduced into the passenger compartment.
Generic air conditioning systems that have coolant/air heat exchangers which draw their heating power from the coolant circuit of an efficient combustion engine of the vehicle drive system are not capable of achieving the temperature levels necessary for heating the passenger compartment to a comfortable temperature when ambient temperatures are low, for example below −10° C. The same is true of systems in motor vehicles powered by a hybrid drive.
Continuous improvements in the efficiency of combustion engine drives and the use of drives that comprise electric motors necessitate auxiliary heating systems to improve the heating of the air in the passenger compartment and hence the comfort of the occupants of the motor vehicle.
Various auxiliary heating systems for vehicle air conditioning systems are known from the prior art. In addition to electric auxiliary heating systems, refrigerant circuits that are operated in heat pump mode are used. For example, glycol/air heat pumps use the coolant from the combustion engine as a heat source. In that case, heat is drawn from the coolant. As a result, the combustion engine is operated for extended periods of time at low temperatures, which has a negative impact on exhaust emissions and fuel consumption. In hybrid vehicles, the intermittent operation of the combustion engine keeps coolant temperatures from reaching a sufficient level on long trips. As a result, the start/stop operation of the combustion engine is suspended when ambient temperatures are low. The combustion engine is not switched off.
Moreover, with fully electrified drive systems, for example in vehicles that are powered by batteries or fuel cells, the waste heat of the combustion engine is eliminated as a potential heat source for heating the air. In addition, the amount of energy that can be stored in the battery of the vehicle is lower than the amount of energy that can be stored in the form of liquid fuel inside the fuel tank. Thus the amount of power that is required for air-conditioning the passenger compartment of an electrically powered vehicle also has a significant impact on the range of the vehicle.
In addition to air conditioning systems that ensure a heating function for the air mass flow to be supplied to the passenger compartment by reversing the flow path of the refrigerant within the refrigerant circuit, the prior art also includes air conditioning systems embodied as compact modules, in which, using a standard refrigerant circuit, any mixing temperature of the air to be supplied to the passenger compartment can be provided by selectively controlling on the air side the functions of heating, cooling, dehumidifying, and reheating.
DE 10 2011 052 752 A1 describes a modular vehicle air conditioning system for heating and cooling air. The vehicle air conditioning system comprises a housing having a blower and dampers for adjusting air flow paths, and a refrigerant circuit having a condenser, an evaporator, a compressor, an expansion element and associated connecting lines. An evaporator air flow path with an integrated evaporator and a condenser air flow path with an integrated condenser are formed in the housing. Fresh air from the environment, recirculated air from the passenger compartment or a mixture of the two can be supplied to each air flow path. The two air flow paths are connected to one another via controllable dampers such that the passenger compartment is heated or cooled solely by adjusting the flow path of the air.
DE 10 2012 108 891 A1 discloses an air conditioning system for cooling and heating the air to be supplied to the passenger compartment and for reheating operation, comprising a housing having two flow channels for conducting air, and a refrigerant circuit having an evaporator and a condenser. The evaporator is arranged in the first flow channel and the condenser is arranged in the second flow channel. The operating mode is adjusted solely by controlling air directing elements. Either the evaporator or condenser heat exchanger is arranged with a part of its heat transfer surface in the first flow channel, with the respectively other heat exchanger being arranged similarly in the second flow channel.
Thus in air conditioning systems embodied as compact modules, a warm air flow conducted over the heat transfer surface of a condenser and a cold air flow conducted over the heat transfer surface of an evaporator are mixed according to the desired delivered air temperatures. After cooling and/or dehumidifying, the cold air flow can also be conducted over the heat transfer surface of the condenser and thereby reheated. During reheating operation, the air to be supplied to the passenger compartment is cooled and thereby dehumidified, and is then slightly heated. In this operating mode, typically less reheating power is required than the cooling power that is required for cooling and dehumidifying the air.
The conditioned air is conducted through an air distribution system having various air outlets and outlet control elements to corresponding air outlets, such as at least one air outlet directed toward the windshield, one air outlet directed toward the occupants and one air outlet directed toward a footwell, into the passenger compartment. Excess air is discharged from the air distribution system through additional air outlets into the environment surrounding the motor vehicle.
However, air conditioning systems that are embodied as compact modules and controlled on the air side require a vehicle architecture that is modified substantially from that of known motor vehicles, therefore they cannot be used in conventional motor vehicles.
In air conditioning systems that are controlled on the refrigerant circuit side in combined cooling and heat pump operation for heating, cooling and dehumidifying the air to be supplied to the passenger compartment and conditioned, the refrigerant circuits in particular typically have a multiplicity of components, such as switchover valves. The refrigerant circuits are highly complex, resulting in high costs and high technical effort. In addition, the capacity of these air conditioning systems, particularly at low ambient temperatures, is not sufficient to ensure the desired comfort of the occupants of the passenger compartment.